http://arxiv.org/abs/astro-ph/0603204 Getting a kick out of numerical relativity John G. Baker, Joan Centrella, Dae-Il Choi, Michael Koppitz, James R. van Meter, M. Coleman Miller 15 pages, 2 figures, submitted to ApJ Letters "Recent developments in numerical relativity have made it possible to follow reliably the coalescence of two black holes from near the innermost stable circular orbit to final ringdown. This opens up a wide variety of exciting astrophysical applications of these simulations. Chief among these is the net kick received when two unequal mass or spinning black holes merge. The magnitude of this kick has bearing on the production and growth of supermassive black holes during the epoch of structure formation, and on the retention of black holes in stellar clusters. Here we report the first accurate numerical calculation of this kick, for two nonspinning black holes in a 1.5:1 mass ratio, which is expected based on analytic considerations to give a significant fraction of the maximum possible recoil. Our estimated kick is 105 km/s with an error of less than 10%. This is intermediate between the estimates from two recent post-Newtonian analyses and suggests that at redshifts z > 10, halos with masses < 10^9 M_sun will have difficulty retaining coalesced black holes after major mergers."